Hitherto, as a blower fan mounted on a ceiling-concealed type air conditioning apparatus, a turbo fan in which a blade of a fan is formed in a three-dimensional shape has been widely employed. For example, a blade is disclosed in which the position of a joint end on a side plate side from a front edge to a rear edge is shifted to a rotation direction A with respect to a joint end with a main plate (a virtual line that connects the front edge and the rear edge is inclined with respect to a radial line), and a shroud end on the front edge side of the blade is inclined to the rotation direction A side (see patent Literature 1, for example).
By forming the turbo fan as above, an end portion on the shroud side on the blade front-edge side where an axial velocity component in inflow air becomes particularly large is inclined to the rotation direction A side and follows an inflow direction of the inflowing air, separation of air which may easily occur in a counter-rotation direction can be prevented and improvement in performance and noise reduction can be realized.
Also, a turbo fan is disclosed, for example, in which a first tangent line tangent to the rear edge at a connection position (first connection position) between the main plate and a rear edge portion of a blade extends so as to become close to the shroud in the rotation direction A side of the blade and a second tangent line tangent to the rear edge at a connection position (second connection position) between the side plate and the blade extends so as to become close to the main plate in the rotation direction A side of the blade (see Patent Literature 2, for example).
By forming the turbo fan as above, a turbulent noise caused by an air-flow velocity difference at an impeller outlet can be reduced.
Moreover, for example, a turbo fan with a serrated rear edge portion of the blade is disclosed (see Patent Literature 3, for example).
By forming the turbo fan as above, compared to those with a straight rear edge portion, pressure gradient and velocity loss of an air flow by merging of flows at the rear end portion becomes smaller, and the turbulent flow is suppressed thus achieving reduction of noise.